This invention is directed to materials for the drilling of and production from wells, especially oil and gas wells. More particularly, this invention is directed to compositions for inclusion in circulating and non-circulating fluids useful in the drilling for and production of oil and gas from wells.
Circulated fluids for use in the drilling of subterranean wells are complex suspensions or fluid emulsions. The purpose of the circulating fluids is manifold in that the fluid serves to cool and lubricate the drilling apparatus, to carry cuttings away from the drill bit to the surface, and to control downhole formation pressures and conditions. Due to the diversity of geological formations encountered in oil and gas recovery, drilling fluids require frequent maintenance; they are usually custom-blended to provide the specific rheology and other properties required for each situation. In recent years, the tendency has been towards the drilling of deeper wells. This tendency has increased the demands placed upon drilling fluid performance in that significant formation variation is often encountered in a single well and that the overall temperature range experienced during drilling can become quite high--often exceeding an order of magnitude. Additionally, the increased depth of certain wells and the tendency for oil and gas to be sought for in regions having substantial geologic pressures, place stringent demands upon drilling fluids. Thus such fluids must increasingly be capable of performing under conditions of high temperature, high density and high salt content.
Non-circulating fluids useful in the recovery of oil and gas are generally employed subsequent to the initial drilling of a recovery well. Such fluids include completion and workover fluids, packing fluids, fracturing fluids, stimulation fluids, water retention agents useful in connection with drilling cement, and other fluids. Each of the foregoing types of non-circulating fluids require certain, well-known properties for good effect. As with circulating fluids, non-circulating fluids are frequently tailor-made or custom-blended to meet the particular requirement of a particular well or geological formation, and each must be capable of utility under increasingly stringent conditions.
The foregoing and other fluids for use in the drilling for and production of oil and gas and in other well-drilling applications are well-known to those skilled in the art. Moreover, the qualities which are necessary to insure good performance in each of the foregoing fluids are similarly well-known. Further explanation of those properties and of fluids which are useful in the production of oil and gas may be had from a review of the publications, Composition and Properties of Oil Well Drilling Fluids, 4th Ed., G. R. Gray, Gulf Publishing Co., Houston (1980); and Drilling and Drilling Fluids, Developments in Petroleum Science, 11, Chilingarian et al., Elsevier, N.Y. (1981), each of which is incorporated herein by reference.
In order to provide circulating and non-circulating fluids for use in the production of oil and gas, it is desired to employ materials which are capable of providing beneficial rheological and other properties to such fluids. It is of principal importance that such materials be capable of providing defined viscosities over a wide range of downhole conditions including extremes in temperature, pH, pressure, salt content, and geological conditions. At the same time, materials for preparation of circulating and non-circulating fluids most desirably should be compatible with other fluid components and adducts, such as clays, surfactants, weighting agents, brines, oleagenous fluid components, and other materials.
Among the principal properties which are desirable to be incorporated in materials suitable for the preparation of circulating fluids is the ability to contribute to viscosity so as to improve, inter alia, the ability of the fluid to remove cuttings from a progressing well. Additionally, such materials preferably are able to seal off porous geological structures through which the well progresses so as to minimize or eliminate loss of circulating fluid to the geological formation. Preferably, such filtration control is not accompanied by irreversible phenomena such that re-exposure of the formation porosity to the well shaft can be accomplished if desired. The foregoing properties are, ideally, maintainable through the extremes of pH, temperature, salt content, etc. which may be experienced in oil field operations. Moreover, such compositions should also exhibit beneficial rheological and filtration control properties in the presence of other common circulating fluid additives and components. Accordingly, compositions which are suitable for the attainment of the foregoing objectives have long been sought by the petroleum production industry.
Non-circulating fluids for oil and gas production also have particularized rheological and other properties which should be exhibited by compositions intended for use in the formulation of such non-circulating fluids. Thus, for example, fracturing fluids should be capable of suspending propping agents through the maintenance of high viscosity and gel strength, which viscosity and support is maintained under conditions of high pressure and throughout the range of conditions which may be experienced downhole. Completion and workover fluids have other requirements which are well-known to those skilled in the art including the need to maintain viscosity under a wide range of temperatures and other conditions. Those properties which are important to a particular kind of circulating or non-circulating fluid for downhole operations are well-known to those skilled in the art. Reference to the foregoing publications, which have been incorporated herein by reference, will provide further insight into such requirements. Accordingly, compositions which are suitable for the maintenance of viscosity and other rheological properties, for the control of fluid loss to geologic strata, for the suspension of particulate propping agents and the like, for the delivery of acid stimulation media to a formation, for the maintenance of downhole pressure to avoid blowouts through inclusion in weighted fluids, and for the numerous other uses to which oil and gas fluids may be put, all under widely varying conditions, have long been sought by the petroleum production industry.
Numerous cellulosic materials as components for fluids designed for use in conjunction with the production of oil and gas have been used or proposed for use. Cellulosic ether derivatives such as carboxymethyl cellulose, CMC, are known to be useful ingredients of downhole fluids used for oil and gas production. More particularly, CMC has been used as a viscosifying agent or drilling additive to control fluid loss in circulating fluids. U.S. Pat. Nos. 3,446,795, 3,471,402, 3,727,688, 4,043,921, 4,068,720, 4,110,226, 4,110,231, 3,506,644, 3,668,122, 3,954,628 and others disclose carboxymethyl cellulose and related cellulosic materials for such uses. Other hydroxyalkyl celluloses and alkyl ether substituted celluloses have also been used for thickening clay-based drilling fluids and the like. Such materials are chemically modified celluloses which form, in general, water soluble, high molecular weight polymers whose solution properties can include high viscosity. Such modified celluloses are disclosed in, for example, U.S. Pat. Nos. 4,290,899, 4,155,410, 4,169,818, 4,239,629, 4,299,710, 4,096,074, 4,172,055, and 4,239,629.
Cellulosic plant material has been included in certain oil and gas fluids. Thus, U.S. Pat. No. 4,082,677 discloses certain phosphorylated agricultural by-products for use in drilling fluids. U.S. Pat. No. 3,042,608 is directed to the use of ground particulate thermal-setting plastic materials and plant matter as materials for circulation control. U.S. Pat. No. 3,441,528 discloses pentosan-containing lignocellulosics such as seed hulls, bagasse, or corn cobs for the preparation of elastic gels useful as drilling muds. U.S. Pat. No. 2,912,380 is directed to fibrous vegetable materials in conjunction with plastic substances for the control of fluid loss in wells. U.S. Pat. No. 3,788,405 provides plugging of well bore formations by circulation of cellulosic pulps such as wood pulp through the well. Numerous other, prior, formation plugging materials are also disclosed in that patent.
U.S. Pat. No. 3,852,200 discloses microcrystalline cellulose, MCC, as a thickening and gelling agent for the suspension of abrasive particles used in a particular drilling technique.
Certain non-cellulosic vegetable materials and gums have been disclosed in conjunction with oil production fluids. Thus, U.S. Pat. No. 4,142,595 discloses flaxseed gum as a shale stabilizing component of a drilling fluid. Xanthan gum in a calcium chloride, carboxymethyl cellulose completion fluid is disclosed in U.S. Pat. No. 3,625,889. Certain particulate wax compositions are disclosed for fluid loss control in U.S. Pat. No. 3,882,029.
As discussed above, particulate, ground cellulosic substances are known in the drilling art for combating lost circulation in wells. Lost circulation occurs when the proximate formation being drilled is unconsolidated, highly porous, or contains cavernous voids into which drilling mud escapes. Examples of the vegetable materials which have been known for employment to plug such formations include ground wood, ground walnut shells, shredded paper or shredded vegetable matter such as cornstalks, sugar cane, bagasse, or sugar beet pulp. These materials are added to drilling fluids to provide a large particle bridging sealant which alone or in combination with smaller particles plugs porous and fractured formations. Such materials can also be used as an inexpensive bulk filler for naturally occurring voids.